Isoenzymes of pyruvate kinase from mouse liver and mouse hepatoma livers, from human liver and cancerous human liver, and from yeast will be isolated and characterized. The chemical specificities of these various isoenzymes will be compared using various substrate analogs of phosphoenolpyruvate. The differences in specificities will be used in an attempt to generate a tissue specific irreversible inhibitor of pyruvate kinase. This inhibitor might be of chemotherapeutic use and would also help to elucidate the amino acid sequence and three-dimensional structure of the active site of pyruvate kinase.